This study is designed to answer significant questions concerning the use of expert panels to assess the appropriateness and necessity of medical procedures. Such assessments have become increasingly important to third- party payors, health policy analysts, and practicing clinicians through their use in the development of practice guidelines, utilization review guidelines, and quality assurance guidelines. Because of the incompleteness of the scientific evidence, most authorities agree that it is necessary to add expert clinical judgment to methods that assess appropriateness and necessity. One commonly used method, developed at RAND, has now been used by RAND and others to assess appropriateness for over 20 medical procedures (and necessity for seven procedures). In spite of its increasing use, this method has not been subjected to rigorous reliablity testing, nor have the results obtained by this method been compared to the results obtained using other, perhaps less expensive methods. This study will investigate both of these issues. First, we will conduct three parallel panel sessions for each of two procedures: angiography and hysterectomy. Second, we will conduct a multiple-round modified Delphi mail survey for each procedure. For each procedure. panelists for both the three in-site meetings and mail survey will be drawn from a common pool of experts nominated by specialty societies. Three physicians will lead one panel for each procedure. In this way, we can assess the replicability of results over different panels and methods.